There is a second article set to appear on “evolution-proof” malaria control. I think this whole approach is important, but I certainly don’t consider it “evolution-proof” and I wish the authors didn’t insist on suggesting otherwise. Here’s the thing, folks: Plasmodium would be under selection if you mess around with their vectors. They can evolve, also.

Koella, J.C., Lynch, P.A. , Thomas, M.B., Read, A.F. (2009). Towards evolution-proof malaria control with insecticides. Evolutionary Applications, in press.

As many strategies to control malaria use insecticides against adult mosquitoes, control is undermined by the continual evolution of resistant mosquitoes. Here we suggest that using alternative insecticides, or conventional insecticides in alternative ways might enable effective control, but delay considerably or prevent the evolution of resistance. Our reasoning relies on an epidemiological and an evolutionary principle: (i) the epidemiology of malaria is strongly influenced by the life-span of mosquitoes, as most infected mosquitoes die before the malaria parasite has completed its development; and (ii) evolutionary pressure is strongest in young individuals, for selection on individuals that have completed most of their reproduction has little evolutionary effect. It follows from these principles, first, that insecticides that kill mosquitoes several days after exposure can delay considerably the evolution of resistance and, second, that the evolution of resistance against larvicides can actually benefit control, if it is associated with shorter life-span or reduced biting in adults. If a late-acting insecticide and a larvicide are combined, the evolution of resistance against larvicides can in some circumstances prevent the evolution of resistance against the more effective, late-acting insecticide, leading to sustainable, effective control. We discuss several potential options to create such insecticides, focussing on biopesticides.

Read, A.F., Lynch, P.A., Thomas, M.B. 2009. How to make evolution-proof insecticides for malaria control. PLoS Biology 7: e1000058.

Insecticides are one of the cheapest, most effective, and best proven methods of controlling malaria, but mosquitoes can rapidly evolve resistance. Such evolution, first seen in the 1950s in areas of widespread DDT use, is a major challenge because attempts to comprehensively control and even eliminate malaria rely heavily on indoor house spraying and insecticide-treated bed nets. Current strategies for dealing with resistance evolution are expensive and open ended, and their sustainability has yet to be demonstrated. Here we show that if insecticides targeted old mosquitoes, and ideally old malaria-infected mosquitoes, they could provide effective malaria control while only weakly selecting for resistance. This alone would greatly enhance the useful life span of an insecticide. However, such weak selection for resistance can easily be overwhelmed if resistance is associated with fitness costs. In that case, late-life–acting insecticides would never be undermined by mosquito evolution. We discuss a number of practical ways to achieve this, including different use of existing chemical insecticides, biopesticides, and novel chemistry. Done right, a one-off investment in a single insecticide would solve the problem of mosquito resistance forever.

A while ago I posted about some claims that a snake species had evolved an “unbeatable” predation tactic.

Orgel’s Second Rule and “unbeatable” predation tactics

I also posted about a claim that an antibiotic had been invented to which bacteria could not evolve resistance.

“Everlasting antibiotics”, wanna bet?

Here is the most recent in this series of “I can’t imagine how evolution could occur in this circumstance” silliness.

How to Make Evolution-Proof Insecticides for Malaria Control

Insecticides are one of the cheapest, most effective, and best proven methods of controlling malaria, but mosquitoes can rapidly evolve resistance. Such evolution, first seen in the 1950s in areas of widespread DDT use, is a major challenge because attempts to comprehensively control and even eliminate malaria rely heavily on indoor house spraying and insecticide-treated bed nets. Current strategies for dealing with resistance evolution are expensive and open ended, and their sustainability has yet to be demonstrated. Here we show that if insecticides targeted old mosquitoes, and ideally old malaria-infected mosquitoes, they could provide effective malaria control while only weakly selecting for resistance. This alone would greatly enhance the useful life span of an insecticide. However, such weak selection for resistance can easily be overwhelmed if resistance is associated with fitness costs. In that case, late-life–acting insecticides would never be undermined by mosquito evolution. We discuss a number of practical ways to achieve this, including different use of existing chemical insecticides, biopesticides, and novel chemistry. Done right, a one-off investment in a single insecticide would solve the problem of mosquito resistance forever.

Ok readers, go see their paper, then post ideas regarding how evolution might still occur either in the mosquitoes or Plasmodium to make this not so very “evolution-proof” after all.

Hint: Note the following specifics:

The population genetics model makes the following assumptions:

1. Adult mosquito population size is constant.
2. Mosquitoes do not complete more than ten gonotrophic cycles.
3. The genetic make-up of mating males in any cycle is the same as that calculated for newly hatched mosquitoes in that cycle.
4. Males of all resistant/susceptibility genotypes are equally likely to mate successfully.
5. Females mate once only, in their first cycle, as is the norm.
6. Number of eggs produced per laying female is unaffected by egg paternal genotype.
7. Genotypes of emerging adults joining the population are in the same proportions as the genotypes of the generation of eggs from which they hatch.
8. Resistance is dominant, as can be the case.
9. Costs of resistance are dominant.
10. The proportion of infectious humans is constant.

The feeding cycle model makes the following assumptions.

1. Mosquitoes bite humans randomly and uniformly.
2. Malaria-infected mosquitoes never become uninfected.
3. The proportion of humans who are infectious is constant.
4. A variety of parameters do not change over successive gonotrophic cycles: (i) the background mosquito mortality rate (what Smith and McKenzie call “force of mortality”), which is considered as a constant per-capita daily death rate (i.e. there is no senescence), (ii) the probability of taking a blood meal and (iii) the probability of feeding on a human.
5. Conventional insecticides are instant kill.

I’ll point out again what Orgel’s second rule says: Evolution is cleverer than you are.